The prior art machines for pipe bending now in use are intended either for obtaining pipe coils with convolutions of uniform diameter or for processing short length pipes. Lacking in these machines are means for laying the pipe convolutions into a coil and maintaining a preselected diameter of the convolutions when the length of pipe being bent varies in mechanical property or in cross-section. As a result, the coils produced have convolutions of non-uniform diameter and are not sufficiently compact, while a subsequent use thereof may cause the convolutions to intertwine, which in turn results in pipe breakage, as well as reduction in the rate of processing and in the efficiency of such pipe finishing machines as drawbenches, coiled pipe surfacing apparatus, etc.
A known draw bending apparatus comprises a mandrel holder with a mandrel, a driven drum receiving a pipe being bent, and pipe feed and pipe coil carrying means (cf., e.g., G. V. Rosov "Proisvodstvo trub--Pipe Production" Moscow, the Metallurgia Publishers, 1974, p. 416). However, pipe coils produced by this apparatus have convolutions of non-uniform diameter the value of which, depending on the force applied during draw bending, cross-section and pipe wall thickness, or mechanical properties of the pipe, may be in excess of, or less than, the diameter of the coil carrying drum. The resultant coil lacks compactness, while the pipe convolutions making up the coil tend to intertwine, thereby hampering subsequent coil processing, which is especially the case with pipes of substantial length and small cross-sectional diameter.
Also known is a wire coiler disclosed in U.S. Pat. No. 3,270,979, granted Sept. 6, 1966. The machine comprises a bending assembly including a bending capstain or block, a system of guide and pressure rollers, an electric drive and a coil carrying means. The same disadvantages as those referred to in the foregoing apparatus are generally inherent in this machine. Furthermore, the machine is not provided with a coil laying means to produce tightly packed bundles or packages without the pipe coils being intertwined.
Another known machine for roll bending pipes of short length comprises a carrying frame, a pipe bending assembly and a drive means (cf. A. I. Galperin "Machiny i oborudovanie dlya gnutia trub--Machines and Equipment for Bending Pipes," the Mashinostroenie Publishers, 1967, pp. 34 and 48).
A further prior art pipe bending machine incorporates a pipe feed rate setting means, a bending assembly in the form of a plurality of rollers disposed on a frame, one of the rollers being a bending roller, and a drive for imparting movement to the bending roller in the plane of pipe bending from a form block by means of a follow-up roller and a guide (cf. A. I. Galperin "Mashiny i oborudovanie dlya gnutia trub--Machines and Equipment for Bending Pipes," the Mashinostroenie Publishers, Moscow, 1967, p. 49). The form block of this machine sets the bending roller in a certain position in the plane of bending, although this set position fails to guarantee a preselected radius of the bend when the mechanical properties of the pipe or cross-section thereof vary.
Also, the aforedescribed machine permits the processing of pipes of limited length determined by the length of the form block. Therefore, the machine cannot be used for bending pipes of greater length.